1. Field of the Invention
The present invention relates to an optically variable filter array apparatus suitable for use in selection of WDM signals.
2. Discussion of the Related Art
At present ROADM (Reconfigurable Optical Add Drop-multiplexing) nodes for WDM (Wavelength Domain Multiplex) communication systems are required to offer a sophisticated colorless Add-Drop function, or equivalently the capability of effecting separation and addition of optical signals having desired wavelengths. As exemplary of methods to achieve a colorless feature, there is known a structure using a wavelength variable filter array (TFA) for selecting a plurality of input signals from among input WDM signals. In Japanese Unexamined Patent Publication JP-A 11-23891 (1999) and Japanese Unexamined Patent Publication JP-A 5-196910 (1993) as well, as a wavelength variable filter array structure of conventional design, there is proposed an optically variable filter that utilizes variation in cavity length resulting from an electrical-field effect in a liquid crystal element. Moreover, in Japanese Unexamined Patent Publication JP-A 2000-28931 and U.S. Pat. No. 6,449,410 as well, there is proposed a wavelength variable filter for varying selected wavelengths by exploiting variation in cavity length resulting from mechanical alteration in MEMS. Further, in US 2009/0263142 A1, there is proposed a filter constructed by integrating a multiplicity of filter elements on a waveguide utilizing Thermo-Optical effects (TO effects) exerted by the waveguide. Still further, in Conference paper TuN2 of OFC 2003 by J. Berger, F. Ilkov, D. King, A. Tselikov, and D. Anthon, there is presented a tunable filter constructed of a combination of a diffraction grating and MEMS. In this case, MEMS and input-output optical fibers designed in an array form can be utilized as a TFA.